1. Field of the Invention
The present invention relates to a system for controlling frame collision in a wireless local area network (LAN) constituted by a base station and radio terminals and to communication equipment for the same.
2. Description of the Related Art
In the protocol (CSMA/CA) used in a wireless LAN, when a transmission operation is commenced, a non-communication time of a certain constant time is detected to confirm that the base station or another terminal is not transmitting frames before the frames are transmitted. When a plurality of terminals simultaneously start transmission operations, however, frame collision occurs, the frames are destroyed, and the transmission fails. This makes it necessary to devise certain countermeasures to deal with such frame collision.
As will be explained in detail later by referring to FIG. 12 to FIG. 18, the system for controlling frame collision of the related art suffers from the problems that when frame collision occurs, a terminal can not retry transmission until a time-out of an answer frame and that when a base station starts a transmission operation during the frame collision, the base station cannot transmit frames until detecting the non-communication time after an end of the colliding frame.
Accordingly, in consideration with these problems, an object of the present invention is to provide a system for controlling frame collision enabling a transmission retry earlier and the transmission of data frames from a base station earlier.
To attain the above object, the present invention provides a system for controlling frame collision in a wireless LAN constituted by a base station connected to a cable LAN and a plurality of terminals performing radio communication with the base station, wherein each terminal is provided with an adding means for adding a frame start code and a length to a tail end of a data frame to be transmitted from the terminal to the base station and wherein the base station is provided with a collision detection means for recognizing occurrence of collision with respect to a terminal from the base station where the frame start code and length remain without being destroyed in any data frame when data frames simultaneously arrive from a plurality of terminals.